In a heterogeneous wireless integrated network that includes a mobile terminal including a plurality of types of wireless access interfaces, a method has been proposed to seamlessly switch the wireless access interfaces used by the mobile terminal.
If an IP sub network is changed by switching of the wireless access interfaces, then an IP address used by a mobile terminal is changed with the movement of the mobile terminal, and a communication session is disconnected. In this case, the communication session can be held by a Mobile IP (Non-Patent Literatures 1 and 2).
If the Mobile IP is used, a real IP address (care-of address) is allocated to each interface of the mobile terminal. In addition, an IP address (home address) common to all the interfaces is allocated to each interface of the mobile terminal.
A communication-partner terminal identifies the mobile terminal based on the home address of the mobile terminal, and a home agent in an IP network converts the home address to the care-of address or vice versa. According to Mobile Internet Protocol version 6 (IPv6), the mobile terminal constantly notifies the communication-partner terminal of update of correspondence between the home address and the care-of address so that the communication-partner terminal converts the home address to the care-of address.
Meanwhile, the roaming from one IP sub network to another causes a change in IP address, so that high-speed movement cannot be substantially realized. By contrast, movement of a terminal within the IP sub network causes no change in IP address, so that high-speed movement can be realized. Considering these, a network configuration has been proposed, in which each IP sub network is extended as widely as possible and a plurality of heterogeneous wireless access points are accommodated in one IP sub network (Non-Patent Literature 3). According to the Non-Patent Literature 3, at the time of switching of interfaces (hereinafter, “interface switching”), the terminal requests each of the network and the communication-partner terminal to update a correspondence table between a media access control (MAC) address and an IP address.
If the IP sub network is not changed by the interface switching, the network can be configured so that the IP address used by the mobile terminal is not changed according to the movement of the mobile terminal. Such an unchanged IP address is referred to as “common IP address”. A technique has been proposed, in which virtual interfaces obtained by virtualizing a plurality of interfaces each allocated the common IP address are defined to obscure the interfaces switching from a higher application (Non-Patent Literature 4).
Although unrelated to the heterogeneous wireless integrated network, a technique has been proposed to accelerate intranetwork switching speed (Patent Document 1). In such a technique, a layer 2 switch manages not only a real MAC address of each terminal interface but also a temporary MAC address of each terminal interface compressed to have fewer bits sufficient to identify the terminal interface accommodated in the network. When a layer 2 edge switch transmits or receives a MAC frame, intranetwork switching of the interfaces can be performed based on the bit-compressed temporary MAC address by replacement between the real MAC address and the temporary MAC address.
Non-Patent Literature 1: C. Perkins, “IP Mobility Support” IETF RFC2002, 1996/10, pp. 8-11
Non-Patent Literature 2: D. Johnson et al., “Mobility Support in IPV6” IETF Internet Draft draft-ietf-mobileip-ipv6-24.txt, 2003/6, pp. 15-19
Non-Patent Literature 3: Masahiro Kuroda et al., “Study of Layer 2 Mobility Network”, IPSJ (Information Processing Society of Japan) Technical Report, MBL-26 (3), Sep. 25, 2003
Non-Patent Literature 4: Kaouthar Sethom et al., “Adaptation Interface for Seamless Handover between 802.20 MBWA/802.11/802.15”, C802.20-03-104
Patent Document 1: Japanese Patent No. 3132426 (Japanese Patent Application Laid-Open No. 11-27310)
However, if the interface switching of the mobile terminal in the heterogeneous wireless integrated IP network is controlled by the Mobile IP as disclosed in the Non-Patent Literatures 1 and 2, the real IP address (care-of address) of each interface is changed by the movement of the mobile terminal. To obscure the change, the concept of a home address is necessary, and someone or some mechanism has to manage correspondence between the home address and the care-of address. If the home agent is responsible for the management, a communication from the communication-partner terminal to the mobile terminal is basically held through the home agent. This disadvantageously causes packet delay, deterioration of band efficiency, and packet loss. On the other hand, if the communication-partner terminal directly manages the correspondence, it is disadvantageously necessary for the communication-partner terminal to directly recognize complicated Mobile-IP signaling procedures. Various extending methods have been proposed for the mobile IP to prevent packet delay, improve band efficiency, and prevent packet loss. However, these methods force the terminal to exercise further complicated signaling control.
As disclosed in the Non-Patent Literature 3, the interface switching within the IP subnetwork can be processed at high speed. However, the terminal needs to occasionally notify the network or the communication-partner terminal of the change of the MAC address. A time lag in the notification causes IP packet loss. Moreover, it is difficult to protect the security of the notification from one mobile terminal to another, so that the notification is vulnerable to DoS attack.
According to the Non-Patent Literature 4, the interface switching is obscured against the higher application using the concept of the virtual interfaces. However, the actually used interfaces are independent of one another. Due to this, during an actual communication, the communication is held using the MAC address allocated to each interface. Generally, the MAC address used for communication is cached by the communication-partner terminal. Therefore, if the interface switching is performed, the communication-partner terminal temporarily transmits a MAC frame to the MAC address of a previously-used (hereinafter, “old”) interface. If the old interface is unavailable, the terminal discards the MAC frame.
The technique disclosed in the Patent Document 1 completely differs in object from the present invention. The technique does not at all support the object of the present invention, i.e., handling of the mobile terminal and the interface switching. Additionally, the disclosure does not mention a method of allocating the temporary MAC address to the terminal safely and dynamically. Due to this, it is difficult to actually use the technique. Moreover, the technique does not at all overcome the problem of MAC level DoS attack solved by the present invention. Furthermore, the disclosure suggests a mechanism in which the layer 2 switch replies the temporary MAC address relative to the IP address. However, it is difficult to construct such an unordinary layer 2 switch.
It is therefore an object of the present invention to achieve a layer 2 switch network system capable of safely providing a high-speed interface-switching mechanism in a layer 2 switch network.